Analysis employing a hydrogen flame ionization detector



A. J. ANDREATCH ET AL '5 Sheets-Sheet 1 Jan. 3o, 1968 ANALYSIS EMPLOYINGA HYDROGEN FLAME IONIZATION DETECTOR Filed March 23 1962 Jan. 30, 1968A. J. ANDREATCH ET AL ANALYSIS EMPLOYING A HYDROGEN FLAME IONIZATIONDETECTOR Filed March 23 1962 5 Sheets-Sheet 2 Jan. 30, 1968 A.J.ANDREATCH ETAL 3,366,456

ANALYSIS EMLOYING A HYDROGEN FLAME IONIZATION DETECTOR Filed March 23,1962 Sheets-sheet s Jan. 30, 1968 A. J. ANDREATCH EI'Al-A 3,366,455

ANALYSIS EMPLOYING A HYDROGEN FLAME IONIZATION DETECTOR Filed March 23,1962 5 Sheets-Sheet 4 H/WF 6 a Mm //h? /o/v /0/ A/ 7a @Ufa/we 95 /Mmf li f /00 MMQMH/W A. J. ANDREATCH ET AL ANALYSIS EMPLOYING A HYDROGENFLAME IONIZATION DETECTOR Filed March 23 1962 5 Sheets-Sheet 5 I 50K /5K/OOK Il( RECORDER 46 CK5886 CK5886 i? /35 /37 /ooou I.

INVENTOR. John Andrectch Anthony William Beveridge Innes A T TORNE YUnited States Patent O 3,366,456 ANALYSIS EMPLOYING A HYDROGEN FLAMEIONIZATION DETECTOR Anthony .lohn Andreatch and William Beveridge Innes,Stamford, Conn., assignors to American Cyanamid, Company, Stamford,Conn., a corporation of Maine Continuation-impart of application Ser.No. 856,596, Dec. 1, 1959. This application Mar. 23, 1962, Ser. No.181,931

14 Claims. (Cl. 23-230) This application is a continuation-in-part ofour application Ser. No. 856,596, filed Dec. 1, 1959, Air PollutionMeasurement, now U.S. `Patent 3,027,241, issued Mar. 27, 1962.

This invention relates to a -method for the continuous analysis of a gasstream for hydrocarbons and halocarbons including compounds containing acarbon to hydrogen bond, and to methods for utilizing a continuous gasanalyzer, for hydrocarbons or halocarbons, particularly for the analysisof the products of combustion of internal combustion engines, includingair contaminated with such products, but including chromatographiccolumn streams, differential analysis, as in `petroleum exploration, orleak detection, acetylene from the action of Water on calcium carbide,for indirect Water analysis, etc. The method includes the analysis ofgas streams or discrete sam-ples containing such hydrogen to carbon -orcarbon to halogen compounds whether direct, as samples of the humanbreath, or indirect as by passing a carrier gas through a sample of bodyfluid, as blood or urine, and using the vapors as a sample. Theelectrical conductance of various flames have 4been the subject of muchstudy. Early work is reviewed by F. L. Tufts, The Phenomena ofIonization in Flame `Gases and Vapors, Physical Review, volume XXII, 193y(1906). This article Ishows that alkali metal salts, such as sodiumchloride, cause conduction in the flame, and are undesirable impuritieswhere llame conduction of other ions is lbeing measured.

The electrical conductivity of a llame has been used as a rectifier, atleast as early `as 1905, Lee lDeForest, United States Patents 824,638,Oscillation-Responsive Device, and 867,878, Oscillation Detector. Theconductivity of a flame 'has been used to detect the presence of allame, Cockrell, United States lPatent 2,112,736, Flame Detector, Mar.29, l1938. The conductivity of a llame has `been `used to measure theair-fuel ratio, United States Patent 2,324,821, Campbell, Measuring andControl Method and Apparatus, July 20, 1943; United States Patent2,511,177, ID. E. Richardson, Apparatus for Measuring `t-he Compositionof a Gas, June 13, 1950; United States Patent 2,622,962, R. R. Lobosco,Automatic Gas Ratio Sampling Device. The use of more sensitive detectorsfor measuring gas compositions at lower carbon-hydrogen concentrations,particularly in conjunction `with a chromatographic column is disclosedby I. G. McWilliam and R. H. Dewar, Nature, volume 181, 177 (1958) andby J. Harley, Nature, volume 181, 177 (1958); and United States Patent2,991,158, I. Harley, Apparatus for the Analysis and/ or Detection ofSubstances by Gas Chromatography, July 4. t1961; and Australian Patent224,504, An Apparatus for Detecting the Presence of Organic Gases andVapours, Oct. 21, 1959, l. G. McWilliarn.

The present system of Ianalysis is ybased upon the electricalconductivity of a burning hydrogen-oxygen jet, to which llame is fed thestream to be analyzed. A high impedauce voltmeter is used to measure theelectrical resistance between the jet and au electrode suspended in thellame. Such a llame detector alone, or in a Abridged system, hassensitivity to measure lless than 5 parts per 3,366,456 Patented Jan.30, 1968 billion of hydrocarbon expressed as methane using laboratorygases. With specially purified gases in all Astreams such as areobtained by passing gas streams over glowing platinum, hydrocarbonimpurities can `be oxidized or cracked if no oxygen is present,nitrogen, oxygen and hydrogen and ambient air may be prepared which hasa very low hydrocarbon content. With such precautions, a sensitivity ofat least as low as 0.1 part lper billion can be obtained. Mostlaboratory gases, and laboratory air contain some hydrocarbons, and suchhydrocarbons increase the noise level.

This very sensitive measurement permits use in detecting `and measuringthe 'hydrocarbon and halocarbon content in dilute streams, and isparticularly useful in analyzing the products of imperfect combustion inthe exhaust streams of internal combustion engines.

The present llame ion detector is not sensitive to carbon dioxide,carbon monoxide, the oxides of nitrogen, carbon disul-de, sulfurdioxide, Water vapor, etc.

The flame ion detector utilizes ions and/or electrons produced incombustion and such ions and electrons are produced lby the rupture ofcarbon to hydrogen bonds and carbon to halogen bonds as for example incarbon tetrachloride, chloroform, methane, ethane, and the like.Conductivity is largely a function of the total carbon present `whichcarbon is in compounds containing carbon to hydrogen or carbon tohalogen linkages. The relative reading is normally a function of thenum-ber of Carbon atoms which have a hydrogen or halogen attached tothat carbon atom, hence per mol of gaseous compound a relative readingof 1 would be obtained for methane, a reading of 2 for ethane, ethyleneand acetylene and ethanol. A reading of 3 would be obtained for propane,propylene, cyclopropane, propanol, etc. A reading of 4 is obtained forbutene, isobutene, butene-l, butene-2, isobutylene, butadiene, butanol,isohutenol, and the like. A reading of about `6 is obtained from hexane,benzene, cyclohexane, etc. The reading for the halogenated hydrocarbonssuch as chloroform or the totally hal-ogenated hydrocarbons such ascarbon tetrachloride is .less than for t'he carbon-hydrogen type ofbonds. Inasmuch `as approximately the same response is obtained yforboth saturated and unsaturated hydrocarbons the present detector' isparticularly useful for analyzing the products of cornbustion of aninternal combustion engine. The relative response is shown in thefollowing table:

TABLE 1.-RELATIVE RESPONSE OF DETECTOR Relative Relative CompoundResponse, Response, Carbon No.

per unit per mole weight Methane 3. 4 O. 95 1 Ethane 3. 9 2. 0 2Ethylene 4. 1 2. 0 2 Acety1ane 4. 9 2. 2 2 Propane 3. 9 3. 0 3Prooylene. 4. 0 2.9 3 4. 3 3. 1 3 4. 0 4. 0 4 4. 0 4. 0 4 4. 1 4. 0 42-butene 4. 0 3. 9 4 Isobut ylene 4. 0 3.9 4 Lil-butadiene. 4. 3 4. 0 4Hexane 4. 2 6. 3 6 Benzene 4. 3 5. 8 6 Cyclohexan 4. 3 6. 3 6 Heptane.-4. 3 7. 4 7 Methanol. 1. 49 0. 83 l Ethylalcohol 2. 6 2. 0 2 Carbontetrachloride 0. 24 0. 64 1 0.40 0. 1 0. 19 0. 40 1 1. 61 1. 75 2 0 0 10 0 1 Nitrous oxide.-. 0 0 0 Carbon disulfide 0 0 1 The products ofcombustion of the internal combustion gasoline engine and diesel engineare blamed for the productionof the smog which is such a problem in airpollution in certain cities, particularly Los Angeles. One of the bigproblems has been the method of measuring both the contaminants in theair and contaminants or unburned organic material in the exhaust stream.In the past such devices as infrared analyzers have been used. Suchinfrared analyzers are quite bulky, require considerable skill to handleand are comparatively slow. The present device has a far greatersensitivity than any previous device known, is fast, economical and easyto operate.

In the analysis of untreated exhaust gases by the nondispersive,infrared, hexane analyzer, the hydrocarbon response is about 1/2 thatobtained by flame ionization. The hexane inared analyzer has a selectiveresponse for hexane type hydrocarbons but has a very low response to thelower olefins, acetylene and the aromatics.

The California standard for hydrocarbon emission, setting an upper limitof 275 p.p.m. hexane as measured by a hexane infrared analyzer isquestionable because it is based on a hydrocarbon measurement which isnot indicative of the true smog producing hydrocarbons. The developmentof a composite infrared detector which was sensitized with benzene,acetylene and ethylene and gave a response which was proportional to thecarbon content. This detector also responded to oleiins, acetylene andaromatics. The response obtained on exhaust gases was 2 to 3 times thatobtained by the hexane detector depending on the mode of engineoperation. The composite infrared detector is not suitable for theanalysis of Vtreated exhaust gases because of interference due to CO2and H2O and insufficient sensitivity.

The flame ionization detector is good for this application because itresponds to all hydrocarbons and has no response to CO2 or H2O. Thetotal hydrocarbon content of a gas is measured on the ame unit bypassing the gas directly into the flame. The analysis may be madecontinuously or periodically.

By measuring products of combustion in a gas stream and then passingsuch an exhaust gas stream through a catalyst system and againmeasuring, the efficacy of the catalyst system to oxidize theunsaturated and other unburnedhydrogen-carbon compounds is easilydetermined. The use of more etfective catalysts or after-burners is onemethod of solving the pollution problem.

As used in this application the term hydrogen-carbon compounds isdefined as those compounds having hydrogen to carbon bonds. Thisincludes nearly all organic compounds.

If the hydrogen-carbon compounds are not slightly volatile, thecompounds can be detected when suspended as a dust, or aerosol, and socarried to the dame of the flame ion detector.

The present detector is sufiiciently sensitive to detect and measurehydrogen-carbon impurities in the air in American cities. This isimportant for deter-mining levels of air pollution and their sources andfor air pollution research. At least small quantities of methane seem tobe a normal constituent of the earths atmosphere at the surface.

The exhaust gases or air containing exhaust gases or other unburnedhydrocarbons may be measured directly to determine the quantity ofhydrogen-carbon containing components present, or it may be passedthrough a chromatographic column to selectively absorb certain of thesecomponents and delay their rate of passage. By using such a system thevarious individual components are separated and analyzed. Thus it ispossible to directly and without preliminary concentration detect andmeasure the individual amounts of methane, ethane, acetyl-v ene,ethylene, butene, butadiene, butane and pentane, etc. where the amountsof each are measured in parts per billion and the totalamount is lessthan 1/10 of a part per lmillion. Such a sensitivity is both unexpectedand most useful. For the first time the present device makes possiblethe direct determination of the hydrogen-carbon components present incontaminated air from which smog is produced. It also becomes possiblefor the first time to determine the relative effects of variouscomponents so that efforts may be made to selectively remove or disposeof the more disadvantageous products before they are released to theair.

Solid carbon compounds which volatilize and decompose at flametemperatures are also measured. Hence, solid carbon compounds orhydrogen-carbon smoke or smog particles which are suspended in the gasstream are included in the measurement. Accordingly, iinely dividedsolids may be either included by permitting them to remain in the gasstream analyzed or may be excluded by collecting them in a fine porousfilter which will remove such solid components.

Care must be used in operating the present instrument to avoid theaccidental release of cigarette smoke or the products of combustion fromstriking matches because both of these common items release sufficientorganic compounds containing carbon to hydrogen linkages into the airthat if air containing such contaminants is introduced into thedetector, spurious readings are obtained.

Because the atmosphere contains some methane, specially purified air oroxygen must be used, and very pure nitrogen and hydrogen for maximumsensitivity. Whereas for many purposes the background can'beelectrically cancelled, a minor variation in the background could belarger than the desired signal. In the usual chemical laboratory, tracesof solvents, or small leaks, or a worker at an adjacent desk or in anadjacent room using a solvent, can drive the instrument off scale ifambient air is perd mitted to contact the ame.

The instrument may be used to analyze ethanol in the breath, blood orurine of suspected drunken drivers or others. Columns may be used todifferentiate between alcohol and acetone or other hydrogen-carboncomponents, and measure the acetone concentration of a diabetic suspect,whether drunk or sober.

Similarly, the instrument may be used for exploration for oil and gas bymeasuring the concentrations of hydrocarbons in a particular area and byplotting the concentrations in an area from the air above the ground orfrom air drawn from beneath the surface of the ground. The areas inwhich a higher hydrocarbon content occurs can be located and such areasare in general indicative of the presence of petroleum deposits beneaththe surface. Of course, allowance must be made for the spillageofpetroleum products on the surface by trespassers.

In the distribution of gas, either natural or artificial, certaincarbon-hydrogen compounds are present. Methane and ethane for instanceare particularly common constituents of natural gas. By measuring themethane and ethane content of the air above a gas pipeline, small leaksin the gas line can be detected. Methane may be present from swamp gasor sewer gas or organic decomposition. Hence the ethane concentration ismore reliable in oil and gas exploration and leak detection.

Similarly, in chemical plants and oil refineries where various plantstreams are being used the total carbonhydrogen content of the streamcan be measured. The device may be used for detecting toxic gases, forinstance, hydrogen cyanide has a carbon-hydrogen bond and activates themeter. Other uses include measuring the vapor pressure of hydrocarbonsor determining the carbonhydrogen constituents in volatile compositionsdirectly or indirectly. A direct measurement of carbon-hydrogencomponents in liquid oxygen is important in missile works. Thedetermination of'traces of acetylene in oxygen or air has been a problemin liquid oxygen plants, in that the input air is often contaminatedwith trace amounts of hydrocarbons. The acetylene iioats as a solid onthe top ofthe liquidl oxygen while the remaining hydrocarbons, beingsoluble in oxygen, are removed. Positive-type infrared analyzers havebeen used in this application, but a llame ionization detector isconsiderably more sensitive. With a second stage of amplication, asensitivity of l0 p.p.b. is obtained. A arne ionization detector candetermine total hydrocarbons or, in combination with a chromatographiccolumn, the various hydrocarbons such as methane, ethane, ethylene, andacetylene can be separated and determined.

The present device may be used indirectly to measure moisture content bypassing a gas stream through the instrument measuring the totalhydrocarbon content, then passing the same gas stream through a calciumcarbide cell, and measuring the additional acetylene present from thereaction of moisture with calcium carbide. A Grignard system can be usedto release a hydrogen-carbon cornpound by reaction with water.

The change in composition of such a nature is particularly easilymeasured by using a bridge system in which the stream before reactionwith calcium carbide is used in one leg of the bridge and after passingthrough calcium carbide in the other and using the signals to opposeeach other thus the difference signal is a function of the acetyleneproduced from the water vapor in the stream.

Chromatographic systems may be used at the head of the detector to alterthe composition to remove components in a predictable order, or releasethe components in a predictable order so that each may be measuredseparately, or by otherwise modifying the gas stream. Similarly, eitherheat or cooling may be used to selectively remove constituents from thestream prior to measurement.

Among such uses would be included checking solvent concentrations in achemical laboratory, a manufacturing plant, or a hospital, particularlythe operating room where ether may be present, or the concentrations ofhydrogencarbon containing gases in coal mines, tunnels, garages, orother areas where explosive levels or toxic levels may develop or inareas where fuels are handled, such as a petroleum renery or aircraftoperation, including aircraft carriers, etc. Paint factories andpainters and others frequently breathe air which may contain tracequantities of hydrogen-carbon containing gases.

ln addition to the safety or explosive question, gas streams in plantscan be monitored to insure that either hydrocarbons are absent as inliquid oxygen plants or that any of the gases in a chemical plant orrefinery are within desired control limits. It is possible to even checksuch small volumes as the contents of a package to be certain that thesolvents used in the paint of the label or as an adhesive is not presentin a quantity which can undesirably affect the taste, odor, or utilityof the package contents.

Not only can the useful gases be analyzed in such plants, but Wastegases ranging from the exhaust or internal combustion gases to the offgases in a petroleum refinery, or brazing atmosphere, or refrigerationleakage can be checked for halogenated hydrocarbons, etc. Where desired,the gases may be run through a chromatographic column to sepa-rate thegases or without a column the dame ion detector can be used to measurethe total concentration. Scrubbers can be used to remove special classesof gases. It is convenient to use a chromatographic column containingglycerine for example to separate aromatic and non-aromatic gases. Thecolumns can contain polar and non-polar solvents or any other class ofsolvent to give a preferred type of separation `and the column may besubjected to a temperature program to accelerate certain classes ofcompounds as, for example, a single column can be used to analyze a widevariety of Ipetroleum cornponents by starting with the column at belowroom ternperature or at room temperature to concentrate methane and thensubjecting the column to a constantly rising temperature so that theless volatile hydrocarbons may be passed through in a reasonable lengthof time. The use of temperature programs to compact the trailing end ofchromatographic analyses is becoming of more importance with thedevelopment of small columns whose heat capacity is such thattemperature programming becomes practical.

The read-out device for indicating concentrations may be linear as, forexample, in chemical analysis work or it may be changed to logarithmicso that a reasonable length of scale can cover an extremely wideconcentration range as would be particularly suitable for determiningthe hydrogen-carbon or lhalogen-carbon vapor content of recirculatedatmospheres such as in a fallout shelter, a submarine, or a spacecapsule.

Hydrocarbon classes can be determined by using selective Scrubbers toremove the desired compounds. The unsaturated hydrocarbon content ofexhaust gases has been determined by this method. An analysis is rstmade of the total hydrocarbon content. A second analysis is then made bypassing a portion of gas through a HgSO4-i-H2SO4 scrubber which removesthe unsaturates leaving only the saturated hydrocarbons. The unsaturatedhydrocarbon content is calculated from the difference. Since theanalysis is made by subtracting two high percentages, the detectablelimit is reduced to i2% of the total hydrocarbon content.

For dynamic sampling, two flame analyzers are used; one to measure thetotal hydrocarbons and a second to measure the saturated hydrocarbons.The unsaturate concentration being the difference.

A dual ame unit is used for the direct determination of unsaturateconcentration. The ionization currents from the two llame burners areelectrically opposed. To one flame is fed the total hydrocarbon sampleand to the other flame is fed the scrubbed sample. The signal output isa direct measurement of the unsaturated hydrocarbons. A linearcalibration curve is obtained with the flame detector for hydrocarbonconcentrations up to 2% carbon, thus the ow rate to each flame can beadjusted so that the signal output for saturated hydrocarbons is zero.The scrubbing agent may be either a solution or may be impregnated on aporous insert solid absorbent. In either case, an equal volume ofinactive material is placed in the flow stream to the second flame. Inorder to keep the dead volume small, the scrubbing agents are usuallyimpregnated on diatomaceous earth. Since the hydrocarbon signal iseliminated and the analysis made from zero, the difference signal may beamplified to measure low concentrations. Lower concentration ofunsaturated hydrocarbons can be measured with the dual detector.

In the past, vapor phase chromatography has been limited by the detectorused n determining the composition or change in composition of theetliuent gas stream. One of the methods which has been used for a longtime is based upon the change in thermal conductivity with the change incomposition of a gas. Others have been based upon the influence ofradiation of the eiluent gas or the change in the heat of the llame whena portion of the carrier gas is burned with a constant stream of a llamesupporting gas such -as hydrogen.

More recently it has been found that a hydrogen flame could have addedthereto the eiuent from a chromatographic column, after which thehydrogen is burned and the conductivity measured of the gas flame.

It has now been found that by using a concentric jet in which the innerjet is hydrogen and the outer jet is an oxygen containing gas, such asoxygen or air, the sample may be burned by adding to either the hydrogenor oxygen containing stream, the gas containing the products to bemeasured. The conductivity of the products of combustion are anindication of the hydrogen-carbon content of the sample.

A concentric jet permits mixing the hydrogen and the oxygen containingstream at a later time, to avoid explosion hazards of mixing oxygen andhydrogen before combustion, also the concentric jet permits easiercontrol of the oxidizing gas than if the ambient air is used to supportcombustion. Air has a hydrogen-'carbon concentration above the thresholdof ysensitivity of the instrument.

The dead space is also minimized so that faster response time isobtained.

For less exacting conditions, a single hydrogen jet gives good results.

In view of the fact that the electrical conductivity of the ame iscomparatively low, an extremely high impedance circuit is used formeasuring; particularly at low concentrations.

Amazingly the conductivity is found to be a straight line function fromless than parts per billon of hydrocarbon expressed as methane to about5% and with some change in curvature the calibration curve is found togive effective measurable results up to at least 40% methane in acarrier gas. This is a most remarkable sensitivity range.

Particularly at the low concentrations of hydrogencarbon orhalogen-carbon a well-shielded, sensitive measuring device is necessary.At higher concentrations the sensitivity need not be so great. For highimpedance measurements well-shielded leads are used to protect theinstrument from stray electrical elds. Similarly, inasmuch as the gridresistor is preferably of the order of magnitude of 105 to 1012 ohms, itcan be seen that all portions subjected to potential are necessarilyofran extremely resistant material in order that leakage currents do notinterfere with measurements.

Without being limited to the specific details set forth inthe preferredexamples, but instead being limited by the invention as expressed in theappended claims, the following figures and examples are given asillustrative of certain embodiments of the new apparatus and its use.

FIGURE 1 is a cross-section view of the combustion apparatus and awiring diagram of the electrical circuit.

FIGURE 2 is a cross-section of the concentric jet assembly.

FIGURE 3 is a wiring diagram and diagrammatic sketch of a bridgedetector system showing a delay line and a calcium carbide unit forwater detection.

FIGURE 4 is a graph showing the millivolts across the cathode resistoragainst methane in parts per million for a grid circuit resistance ofl010 ohms.

lFIGURE 5 is a low sensitivity graph showing the millivolts across thecathode resistor with a resistance in the grid circuit of 106 ohmsagainst methane concentration in percent.

FIGURE 6 is a diagrammatic view of a portable selfcontained form of theinvention, which is particularly adapted to be used as an exhaust gasand smog analyzer.

FIGURE 7 is a chromatogram of a typical gasoline engine exhaust gasthrough this analyzer.

FIGURE 8 shows diagrammatically a double multiple chromatographic orabsorption column system feeding a bridge-type ame ion detector.

In the construction of the present ionization detector it is necessaryto use the fastidious techniques required for extremely high impedancecircuits. Leakage resistances of greater than a million million ohms(l012 ohms) can cause erroneous readings at the higherresistancemeasurements used for the greater sensitivities.

COMBUSTION CHAMBER The burner chamber base 11 is constructed of aplastic with an extremely vhigh insulating value. Preferably it is apolytetrauoroethylene although a metallic base using insulating sleevessuch as glass sleeves may be used. Through this base extends the wiringcircuits and the gas flow tubes. As shown in FIGURE 2, representing apreferred embodiment, the inner jet 12 is mounted on a fuel jet support13. While other materials of construction may be used, a stainless steelhypodermic needle of about 22 gauge makes an excellent inner jet. Theinner needle hub 14 is mounted on the fuel jet support 13 which is apiece of glass or brass tubing of a size to fit the hub of the innerneedle, which in turn is mounted in the burner chamber base 11. It ispreferred that the fuel jet support extend only part way into the burnerchamber base so that the insulating characteristics of the burnerchamber base separate the complete burner assembly from the gas supplylines electrically.

Concentrically mounted on the inner jet is the outer jet 15.Conveniently but not necessarily the outer jet is a hub of a hypodermicneedle concentrically mounted on the hub of the inner needle andsoldered or brazed thereto. Silver soldering is preferred. Preferablythe size of the outer jet is such that the concentric oxidizer orifice16 has an area of at least as great as the gas iiow area ot' the innerjet 12 but not more than 3 or 4 times that area. Into the outer jetfeeds the oxidizer gas line 17. This is preferably metal also silversoldered into the outer jet. An oxidizer gas line elbow 18 as shown inFIGURE l connects to the oxidizer ow port 19 in the burner chamber base.The oxidizer-flow port 19 and the hydrogen flow port 20 in the burnerchamber base are preferably comparatively small holes extending throughthe burner chamber base which are counterbored at the .upper and lowerend. The counterbores at the upper end receive the fuel jet support andthe oxidizer gas line elbow against the shoulders 21 of the counterboredport. By having a counterbore and a comparatively small gas ow port ineach line there is no danger of insetting the fuel jet support or theoxidizer gas lin-e elbow too deeply into the burner chamber base andthereby introducing a high resistance short. The short length of smallsize in the oxidizer flow port and the hydrogen ow port each cut down onthe dead gas space and insure extremely high insulating value. It isdesirable that the dead gas space be kept to a minimum in order thatchanges in sample gas concentrations are reflected in the flow of gasthrough the concentric oxidizer jet and the inner jet as rapidly aspossible, thereby increasing the speed of response of the instrument. Itis preferred that both the inner jet and the outer jet be of stainlesssteel or other corrosion resistant metal. The tops of the two jets arepreferably in the same plane. The jets may be ground at the same time,after assembly, against a grinding wheel, being Careful to avoid theproduction of burrs. By having the jets of the same length the risk ofthe inner or outer jet becoming overheated by contact with the flame isminimized. If either the inner jet or the outer jet becomes overheatedsuch jet may introduce eX- traneous ions into the llame and change thereading of the instrument. Either the inner or the outer jet may be ofglass; but if of glass, the instrument is more fragile and ions releasedby the glass may give false readings. When constructed of metal, in thepreferred embodiment, the risk of differences of potential at differentplaces on the jet assembly is minimized, and the jet assembly isextremely rugged and mechanically stable.

LTo a metallic part of the jet assembly is attached'a burner lead 22.This burner lead is an electrical conductor which passes through theburner chamber base to the electrical parts of the apparatus. Preferablythe burner lead is a shielded lead which is well insulated.Polytetrafluoroethylene insulation is preferred. Other high resistanceplastic may be used as insulation if care is used dury ing assembly toavoid contact of the bare lingers with the insulation as many of theother plastics are more susceptible to fingerprints and the traces ofcontamination from a fingerprint across the insulation of a lead canform a high resistance short which leads to instability in the assembleddevice.

Also extending through the burner chamber base is a collector screensupp-ort 23. Conveniently this collector screen support is an insulatedwire which furnishes both mechanical support to a collector screen 24and serves as an electrical connection to the collector screen. The colllector screen is preferably of a vcorrosion resistant metalv such asplatinum or nickel. The platinum or nickel is spot welded to thecollector screen support at a point outside the riarne above the jet.The collector screen may either be a coil of Wire or a single wire or awoven screen or perforated screen which is placed above the jets in sucha position that the combustion fiame above the jets impinges directlyupon the screen. Conveniently the screen extends beyond the ame in alldirections. The portion extending beyond the flame act as heat radiatorsto keep the screen cool, to avoid secondary emission, and lengthenscreen life. A screen about 1 centimeter in diameter of platinum makes avery satisfactory collector screen. The screen is located at a height offrom about 2.5 to millimeters above the jets. A height of 7.5millimeters gives very good results. The screen height is not critical.Also extending through the burner chamber base are two ignitor leadswhich extend to an ignitor coil 26 which is placed adjacent but not inthe ame. The ignitor coil is preferably a resistance wire which isconnected by the ignitor leads to a suitable power source, for example,an alternating current transformer, to cause the ignitor coil to glowred and ignite the hydrogen jet. A double pole ignitor switch 27 isprovided to disconnect both leads of the ignitor coil from the currentsupply after the anie has been ignited. A spark gap ignitor may be used.

Closely fitting on the burner chamber base 11 is a burner shield 28. Theburner shield is a metallic shield which fits closely on the burnerchamber base and has a foraminous area 29 directly above the burneritself and which shield is grounded. The entire shield may be of wiremesh but conveniently a metallic foil such as an aluminum foil is used,the portion above the jet either being perforated or having a built-inscreen.

For use where the air surrounding the instrument may be contaminated, itis preferred that the burner shield be of a metallic foil through whichextends a ushing air line 30. A gentle current of pure flushing air isfed through this liushing air line to carry away the products ofcombustion and to insure that the air coming in contact with the burnerfrom the outside is free from gases containing hydrogen-carbon orhydrogen-halogen compounds which might give an erroneous reading.

Unless the burner assembly is mounted on and extends into an electricalinstrument box which is itself a shield, it is preferred that anadditional shield extend around the bottom side of the burner chamberbase. This bottom shield 31 has holes in it for the various leads intothe burner chamber 32 formed by the burner chamber base and the burnershield 28. Shields on the collector screen support 23 and the burnerlead 22 may be electrically connected to this burner bottom screen wherethey pass through the screen.

GAS FEED SYSTEM Underneath the hydrogen fiow port 20 is a hydrogensupply line 33. In the hydrogen supply line is a hydrogen how meter 34,a hydrogen capillary flow orilice 35 and a hydrogen pressure gauge 36.Hydrogen is supplied from a suitable source such as a compressedhydrogen tank through a reduction valve to the pressure gauge at thehigh pressure end of the hydrogen capillary flow orilice. The hydrogencapillary ow orifice may conveniently be a piece of thermometer tubingor other tubing having such a small opening that pressure drop throughthe tubing is considerable and the ow a function of the hydrogenpressure on the oriiice. The How can be measured through a liowmeter andadjusted by changing the pressure at the pressure gauge to adjust thehydrogen flow to a desired rate.

A sample T 37 in the hydrogen flow line feeds a sample into the hydrogenand with the hydrogen into the jet.

The hydrogen conveniently has at least some nitrogen mixed with it toreduce the llame temperature. The amount of nitrogen mixed in with thehydrogen depends in part upon the amount or" diluent gases supplied withthe sample. If the sample is comparatively dilute, with a highproportion inert gases, pure hydrogen may be used but if the sample ismore concentrated, pure hydrogen mixed with about 50% nitrogen ispreferred.

Air or oxygen is supplied to the oxidizer jet. The air or oxygen issupplied from a pressure source through an oxygen capillary How orifice38. There is a pressure gauge 39 to measure supply line pressure whichpressure is adjusted so that the rate of flow through the capillary isas desired. An oxidizer ow meter 40 measures the feed rate of theoxidizer gas. Pure oxygen may be used as the oxidizer, but preferably ismixed with at least some nitrogen to avoid too high a flame temperature.The air or oxygen supplied as the oxidizer is desirably comparativelyfree from hydrogen-carbon or hydrogen-halogen containing substituents inorder that there is not an undue background or a false signal due todetectable materials introduced as contaminants with the oxidizer gassupply.

Some hydrogen-carbon substituents may be present in the supplied gases,and be subtracted out on the recording circuit by the zero leveladjustment, if the concentration is constant. The more sensitive rangesrequire better control of background noise, to which such contaminantscontribute. Commercially available pre-purified nitrogen and oxygencontain some hydrogen-carbon substituents frequently from 0.1 to partsper million.

ELECTRICAL SYSTEM The frame polarizing battery 41 is connected so thatthe burner jet is positive and the negative lead from the battery passesthrough a grid resistor 42, to the collector screen support 23 which iselectrically connected to the collector screen 24. A grid resistorselector switch 43 is used to select a grid resistor of the propervalue. The polarizing battery may have a value of from about 15 to 350or more volts. The sensitivity increases rapidly as the voltage isincreased to about volts. Between about 115 and 340 volts thesensitivity is constant. A greater voltage is unnecessary. The value ofthe grid resistor may vary from about one hundred thousand ohms to onemillion million ohms (105 to 1012 ohms). As shown in the FIGURE 1 a goodselection is to have resistor Values selectable at will of 106, 107,108, 109, 1010, and 1011 ohms. A grid resistor is selected which has avalue which gives a good instrument reading with the hydrocarbonconcentration in the sample stream.

The collector screen is connected to the grid 44 of a vacuum tube 45.The vacuum tube is necessarily a high impedance tube. Tubes which areused for electrometers are preferred. A tube such as tube type 5803 orVictoreen VX55 or CKSSSS gives good results. `Such a tube requires aplate voltage of 71/2 to 15 volts, a control grid voltage of about -1.7volts and requires a grid control current in the order of 2X10-11amperes. Such a tube may have an amplification factor (mit) of about 2.0and a mutual transconductance (gm) of `about micromhos. Any standardvery sensitive electrometer circuit may be used. At high concentrationsan ordinary vacuum tube voltmeter can be used.

One, as shown consists of a lament battery 46 wired through asingle-pole double-throw switch 47 to the filament 48 of the tube 45. lnthe cathode circuit of this tube are a cathode resistor i9 and amicroammeter 50. Conveniently the cathode resistor 49 has half theresistance of the microammeter 50 and millivoltmeter recorder leads S1lead to a millivoltmeter recorder 52 so that it may be connected inshunt across the microammeter or the cathode resistor or both to give asensitivity of 1, 2, or 3. Typical values of the microammeter resistanceand the cathode resistance are 2200 and 1100 ohms respectively. A 10millivoltrneter recorder connectable at will across 1,100, 2,200, or3,300 ohms as a cathode resistance gives good stable values. A shunt 53leads around the microammeter and the cathode resistor and is connectedto the seci 'l ond pole of the single-pole double-throw filament switchso that when the filament is disconnected from the battery and theinstrument turned off, the microarnmeter is shunted through the cathoderesistor. By so shunting the microammeter, the needle is damped and themeter is less sensitive to mechanical injury during handling.

A stabilizing resistor 54 shunts the filament battery to the cathoderet-urn. The negative end of the battery is conneced to the cathode leadand by having the stabilizing resistor 54 in series with the cathoderesistor and the -microammeter, as a shunt lto the filament battery7 aslight positive bias is introduced .by this filament battery circuit tothe cathode return and greater stability of calibration is therebyobtained. A value of about 15,000 ohms on the stabilizing resistor givesgood results.

A plate battery 55 is connected through a plate current switch 56 to theplate 57 of the vacuum tube. The plate return is connected through themain cathode bias resistor S to the microam-meter and through themicroammeter and smaller cathode resistor 49 to the negative side of thefilament. A value of about 50,000 ohms gives van adequate cathode bias.The plate battery and plate current switch are shunted by a plate shuntresistor 59 and a zero potentiometer 60.

For greatest sensitivity the entire polarizing battery circuit should beshielded by a shield 61, using shielded wires and an actual shield overthe battery. Such shielding gives greatest sensitivity and stability. Y

As will be obvious to those skilled in electronic work, the shields maybe omitted for lower sensitivity work, with a slight loss in stability.Similarly for convenience the plate current switch 56 and the filamentswitch 47 may be ganged.

The flame polarizing battery may have a switch in its circuit but inview of the extremely high impedances involved this battery has shelflife whether it is switched on or off, and the flange itself act-s as yaswitch.

Sources of electrical potential other than a battery may obviously beused in the apparatus but in view of the extremely high stabilityrequired such other potential sources would be unduly bulky and for thevery small current required batteries furnish the most economical andportable source of power. The `entire assembly is very small, isconvenient and may be made portable for use in measuring hydrocarbonsubstituents in various areas or may actually be airborne as by aballoon for measuring smog at various altitudes over a city, a suitabletransmitting system being used to give an indication by radio of theindicators readings.

Great care must be used in the grid circuit of the electrometer tube toavoid high resistance shorts. For example, the grid resistors arepreferably sealed in glass, and the glass shields are carefully washedand then handled only by forceps during manipulation including solderinginto the system. The grid resistor selector switch must be one which hasan extremely high resistance and is preferably of ceramic orpolytetrafiuorethylene construction in order that the resistance throughthe switch will be of the same order of magnitude as in the rest of theequipment.

Although sample introduction is shown into the hydro- -gen jet, thesample may be introduced with the air or oxygen jet. A sampleintroduction with the oxidizer gives results which are excellent,although results obtained when introducing the hydrocarbon with thehydrogen are preferred. Usable results are obtained at lower sensitivityeven if the leads and potential to the flame is reversed. Greatersensitivity is obtained when the flame jet itself is the positive pole.

BRIDGE CIRCUITS As shown in FIGURE 3 two of the flame ion detectors maybe connected in a bridge circuit. Whereas, other bridges may be used,one satisfactory circuit involves connecting two of the jets andcollector streams in series.

As shown in FIGURE 3, a flame polarizing battery 62 is connected acrosstwo flame ion detectors 63 A and B, with the tjets and screens arrangedin series. The high resistance potentiometer 64 is connected across theflame polarizing battery 62 bridging the llame ion detectors. To the midpoint of the potentiometer 64 and the central jet-screen connector 65 isconnected an amplifier 66. A battery switch 67 provides fordisconnecting the flame polarizing battery.

A mixture of hydrogen and nitrogen is supplied as a fuel and diluent andoxygen is supplied as an oxidizer, the same supply system being used tosupply equal quantities of these gases to each of the flame iondetectors A and B. The sample is supplied and injected Yinto theoxidizer supply of detector A directly', and through a calcium carbidecell 68 and then into the oxidizer supply of detector B. The sample maybe supplied from any suitable source. The first detector gives animmediate reading of the hydrocarbon content of the sample stream. Thesecond one gives a delayed reading due to the time required to gothrough the calcium carbide cell. If a dry sample is supplied the delayin passing through the calcium carbide cell and the longer supply linecauses the detector B to give a somewhat later reading. Therefore thedifference between the reading of A and B as measured on the bridgecircuit is indicated by the amplifier as the rate of change ofhydrogen-carbon components in the sample stream. If the sample stream isconstant and contains moisture the calcium carbide reacts with themoisture to deliver acetylene and the additional concentration of theacetylene is measured on the amplifier.

Obviously, a simple delay line may be used instead of the calciumcarbide cell to give a reading of rate of change of the hydrogen-carboncomponents or an equivalentdelay line may be introduced into the supplyline of detector A so that the bridge is sensitive to only moisturecontent as the time of injection of the sample is adjusted to be equal.Other modifications of the bridge circuit may be used for other purposeswhich may be desired using the ideas embodied above.

EXHAUST GAS AND SMOG ANALYSIS FIGURE 6 shows an embodiment of thepresent flame detector particularly suitable for analysis of exhaustgases from combustion engines such as automobiles and for analysis ofsmog producing constituents in the atmosphere. In this embodiment theflame detector chamber itself 69 which may be as shown in FIGURE 1 isconnected to an amplifier and recorder 70. The circuit shown in FIGURE 1may be used or the microammeter alone may be used as a readout device.The oxidizer source used is pure oxygen or air from an oxidizer supplytank 71 which is under high pressure. The oxygen or air passes throughthe oxidizer control valve 72, past an oxidizer pressure gauge 73through an oxidizer flow control capillary 74 and an oxidizer flow meter75 to the flame ion detector.

Hydrogen is supplied from a hydrogen pressure tank 76 through a hydrogencontrol valve 77 past a hydrogen pressure gauge 78 through a hydrogen owcontrol capillary 79 through a hydrogen flow meter 80 to the burner jetof the flame ion detector.

Nitrogen under pressure is supplied from a nitrogen supply tank 31through a nitrogen control valve 82 past a nitrogen pressure gauge S3.

The nitrogen is passed through a stream selector T- Valve 84. The outputsystem from this stream selector T-valve passes through a sample streamow control capillary S5 to a manifold 86.' A sample flow meter 92 isinserted before the manifold to show the ow rate ofy the stream.

Also connected to the manifold is a sample port 87. Conveniently, thisis a T-joint into the ymanifold with a rubber closure, such as is usedfor injectible drugs, and which has a rubber member designed to bepunctured by a hypodermic needle. Samples of gases can be injected froma hypodermic syringe by running the needle through the sample port 87into the manifold and injecting the gas into the owing nitrogen.

Also connected to the other arm of the stream selector T-valve 84 is acontinuous sample flow line y88. A sample pump 89 supplies a continuoussample stream, from any source, past a sample pressure gauge 90 to thecontinuous sample ow line 88. A bleed valve 91 is provided to releasesurplus gas to control pressure. The sample stream flow rate iscontrolled so that either the flow rate of a carrier nitrogen stream, orfrom a sample pump is a desired value.

The metered flow passing from the manifold 86 passes to a selectorT-valve 93, which passes the sample stream selectively through a silicagel column 94 or a by-pass 95 to an output T-valve 96, which feeds thesample stream into the hydrogen dow by a connector 97. The two T- valves93 and 96 are operated so that a sample is selectively passed eitherdirectly through the by-pass 95, or through the silica gelchromatographic column 94 to the hydrogen stream to the flame iondetector.

A stream sample, for continuous analysis, or a single shot sample, fedby a hypodermic syringe to the nitrogen stream, may thus be eitheranalyzed directly for total hydrogen-carbon compounds, or passed througha chromatographic column, so that in-dividual components may be measuredindependently.

This embodiment is particularly convenient for -portable use as theoxygen, hydrogen and nitrogen tanks may be small laboratory size tanks,the sample pump may be a hand operated pump and the entire device isportable and may be easily carried from place to place. The entiredevice may be carried by a balloon for measuring contaminants at anydesired atmospheric level.

An oxidizer by-pass 98 may be provided to pass part of the air or oxygenfrom the oxidizer supply tank 71 past a secondary air valve 99 through asecondary air capillary 100, through a secondary air ow meter 101 to thecombustion chamber of the llame ion detector. For use where the ambientair is low in hydrogen-carbon compounds, a simple Ventilating port may-be used, but controlled surrounding conditions for the burner jet arepreferred for high sensitivity measurements, as the impurities in thesurrounding air also give a response. Side vents in the outer jet may beused as bleed ports to supply a controlled secondary air, but anindependent supply line gives better flow control. Similarly the gascontrol valves may be simple needle valves, but pressure regulatorvalves are easier to manipulate for accurate control of the iiow of thevarious gas streams.

USE OF ANALYZER The analyzer shown in FIGURE 6 may be used for measuringvery low concentrations of hydrocarbons. Conveniently, a sample fromeither the exhaust of an automobile or from air which is suspected ofbeing contaminated is passed through the sample pump, mixed with thehydrogen, fed to the dame jet, and burned in the oxygen from the oxygenor air tank. The ratio of hydrogen flow in milliliters per minute tototal gas flow in milliliters per minute should be below 0.58.

The response varies with the ratio of hydrogen to the diluting gases. Aratio of hydrogen to inert gas, plus oxidizer, of about 0.85 to 0.9, ona volume basis, gives the least variation of signal with a slight changein gas flow rates. A fairly flat plateau exists between a ratio of 0.7to 1.2. Values outside these ratios give reproducible results but theinstrument is less stable. Obviously helium or other inert gas may beused as the diluent.

An excess of oxygen is normally supplied.

The hydrogen flow rate for a 22 gauge needle jet may be from l to 50milliliters per minute, and 25 to 35 gives preferred results. The ratioof hydrogen to other gases is more important than the absolute dow rate.

The gases arewell mixed in the flame, so that the sample can be injectedinto either the hydrogen or the oxidizer jet. At least part of theoxygen may be mixed in the hydrogen jet. Such operation is convenientwhen part of the sample stream is oxygen. Flame instability resultsIfrom too high a ilow rate in the jets or too high a dilution of thehydrogen with inert gas and increases background noise.

If a reading of a particular sample is desired, the sample is runthrough the sample pump, directly through the bypass, mixed with thehydrogen, and burned in the jet and the potential measured. The ame iondetector is calibrated against known samples of approximately the sameconstitution under the same conditions. The response is proportionate tothe number of carbons having carbon to hydrogen linkages or carbonshaving carbon to halogen linkages. Note Table 1. The exhaust gas of anautomobile or the atmospheric air may be measured for smog in thisfashion. If it is desired to determine what are the constituents ofsmog, atmosphere, or exhaust gas, the T-valves 93 and 96 are turned topass the sample through the silica Igel column, a selected sample isinjected by a hypodermic syringe, passed through the silica gel columnand into the nitrogen stream. The gas then passes through the silica gelcolumn, and develops the absorbed hydrocarbon constituents. Methaneitself passes almost directly through the column while the higherhydrocarbons pass through more slowly. A typical analysis is shown inFIGURE 7 in which the first peak is methane, the second one ethane, thethird ethylene, the fourth acetylene and the fifth propylene. A silicagel column a quarter of an inch in diameter and 8 inches long gives gooddevelopment. The silica gel column may be heated to insure thevolatilization of higher hydrocarbons, or the column may ybe longer orshorter depending upon the discrimination desired -between sampleconstituents. In each instance a ow of oxygen, hydrogen and nitrogen ismaintained constant by use of the appropriate control valve to controlthe pressure of the gas forcing the gas through the ow control capillaryand the ow meter.

The present device is suliiciently sensitive to measure impurities inordinary city air. For example, the methane content in a laboratorybuilding was found to be about 3 parts per million.

Typical values of hydrogen-carbon 'oonstitutents in city air, in NewYork City was found to be 7.6 parts per million, calculated as volumesof methane per volume of air. Of this 2.2 parts per million weremethane; 0.08 part per million of ethane (0.16 methane equivalent); 0.11part per million pentane, and 0.13 part per million hexane.

In Stamford, Conn., in a country area, a value of 1.4 parts per million,reported as methane was obtained.

The area under the curve in the etiiuent from a chromatographic columnis a measure of the amount of the particular constituent present in thesample. Either a continuous analysis or a selected sample analysis maybe made. If a continuous analysis is used the signal response is ameasure of a concentration of the sample gases containingcarbon-hydrogen or carbon-halogen linkages.

In each instance the device is calibrated against known samples. Therates of gas iiow and the exact physical configuration and sensitivityof the circuits is such that the sensitivity cannot be theoreticallydetermined. However, known samples are run through the burner and acalibration curve established which remains constant for the particularinstrument and flow rates being used.

FIGURE 4 shows a response expressed in millivolts across a cathoderesistor of 1,100 ohms against the methane content in parts per millionof a sample gas (air) being introduced in the device of approximately 35milliliters per minute in the outer jet and a hydrogen flow of 30milliliters per minute through the inner jet. A grid resistance of 1010ohms was selected.

Approximately the same calibration curve is obtained 15 if the samplegas, in this case air containing methane, is mixed with the hydrogen andfed to the single inner jet, and the outer jet is not used.

The same instrument at a much higher methane content gave the responseshown in FIGURE in which the sensitivity is diminished by using a ohmresistor in the grid circuit of the tube. At the lower concentrationsthe response is seen to `be linear with concentrations. Atconcentrations above about 1% of methane, the curve no longer is linearbut is reproducible up to values of at least 40% methane. Moreconcentrated gases can be diluted.

Gases other than methane are used for calibration for the measurement ofthe concentration of such other gases. If a constant rate is to be usedfor a flow sample, the rej sponse is proportional to the total number ofcarbons containing hydrogen linked thereto, plus the value of thosecontaining carbon with halogen linked thereto. The hydrogen-halogencalibration constant is slightly smaller; separate calibration isrequired for the halogen components. For straight hydrocarbons theresponses thus are twice as great per mol for ethane as for methane,three times as much for propane and so on proportionally upward.Obviously, the Vapor pressure of the sample gases must be such that theywill remain in their vapor form and not condense out as liquids in theapparatus. If higher concentrations of higher hydrocarbons are used theentire apparatus may be warmed in a suitable oven to a temperaturesuiiiciently high to keep the sample in the vapor form. Calibration onmethane alone gives values which are satisfactory for determination ofthe contents of gases containing hydrocarbon linkages. Where achromatographic column is used to differentiate between gases, acalibration sample may be used to determine where each sample comes olfof acolumn and to synthesize a sample approximately that of the unknownsample to check and be sure that all of the peaks are as anticipated.With the more complicated samples which are found in smog, at timescertain of the constitutents overlap on the column and are diicult toseparate. Longer columns can solve this difficulty.

DIFFERENTIAL ANALYSIS The apparatus shown in FIGURE 3 is used fordetermining concentration gradients. Even if the air in the laboratoryis contaminated or even if the source of oxygen has a certain amount ofhydrocarbon vapors in it, still accurate readings may be obtained usingthe bridge circuit. Using the bridge shown in FIGURE 3 a delay line maybe used and the apparatus carried along the ground. For pipe line leaksa short delay of about 5 seconds is useful, as the concentrationgradients are sharp. For oil and gas exploration a delay of at least 2minutes is useful, or an absolute concentration plot may be used. Thevariations in hydrocarbon content of the ambient air as it comes fromvery close to the ground can 1be plotted to give a measurement of thelikelihood of underground deposits containing gases being found.Similarly, samples of air passed through water samples from variouslocations in a body of water are analyzed to give hydrocarbon -contentof the water, as an indication of underwater oil and gas deposits.Ethane is a more reliable indicator than methane, as marsh gas containsmethane. Similarly, a delay line may be used to show the variation inhydrocarbon content as motor vehiclesV pass a given point or as theinstrument is carried away from a highway serving as a source ofcontamination.

The same instrument may be used with the calcium carbide tube in placeto determine the moisture coutent. Inasmuch as a calcium carbide reactswith Water, concentrations of Water in gases can be measured ateXtremely low concentrations. The calcium carbide should be fresh sothat an earlier history of moisture contamination does not disturb theaccuracy of the apparatus.

Using the apparatus of FIGURE 3, 30 milliliters per minute Q hydrogen isfed to each inner jet. milliliters 16 per minute of oxygen is fed toeach concentric oxidizer jet. A sample of 20 milliliters per minute ofair is also introduced in the outer stream.

The signal in the rst ion detector is a measure of hydrogen-carbonconcentration, and may lbe measured if desired. The additional signalfrom the second jet, as

shown on the bridge indicates additional hydrogen-carbon, as acetylenefrom the reaction of calcium carbide with moisture in the air. Amoisture content of room air of 1.5% is found on a typical day. Themoisture can be measured even in very dry streams from drying equipment,when values of 0.1 part per million can be measured.

In order to test for ethyl alcohol in human breath, blood or urine, achromatographic column is desired in order to discriminate betweenethanol, acetone, hydrocarbons or other organic material. A 20%kpolyglycol on 70 to 100 mesh diatomaceous earth chromatographic column,IA" diameter and 6 inches long, at room temperature permits detection ofboth acetone and ethanol. The sample is taken by blowing breath into aclean glass syringe, or bottle. The sample is then injectedV into thecolumn as shown in FIGURE 6, except for the column Y filling. Acetone iseluted in 45 seconds and ethanol is eluted in three minutes. Vtith thesensitivity and selec-V tivity of the analyzer, it is possible tomeasure the alcohol content in the breath 2 hours after drinking oneounce of liquor. It is also possible to distinguish a diabetic coma fromalcoholism in a patient by measuring the acetone. Using a single jet,burning in filtered room air, a hydrogen ow rate of 25 millliters perminute and a nitrogen'flow rate of 35 milliliters per minute, and theabove mentioned 6 inch polyglycol on diatomaceous earth column, with a 5milliliter sample, using a l01o ohm grid resistor and a calibratedscale, the results showed an alcohol Content of od scale at 3 minutes,2.5 rnillivolts equal to l0 parts per million of ethanol in air at 16minutes; 0.95 millivolt,

equal to 3.7 parts per million after 20 minutes, and 0.4

Time, minutes: Concentration ethanol, p.p.m.

In a second experiment the same subject drank 10 cc. of 100 proofethanol. The mouth was not rinsed with water. The breath from the mouthwas found to contain:

Time, minutes: Concentration, p.p.m.

In a third experiment with the .same subject 30 cc. of the same V proofethanol was ingested and the concentrations were found to be:

Time, minutes:

If the same tests are run using a good grade of bourbon whisky, methanolcan be detected in the breath. Good Concentration, p.p.m.V

bourbon contains in the order of 200-300 parts per million of methanol.This is sufficient for a distinct methanol peak to be located in thechromatogram run from the breath of a subject drinking the bourbon.

The acetone concentration of the subjects breath remained at about 0.5p.p.m. throughout.

Cigarette smoke contains methanol, ethanol, acetone, and many othercompounds. The detection of ethanol from other sources can be partiallyobscured by these peaks if the subject is smoking.

The resolution of peaks can be increased by longer columns, and greatersensitivity, so that volatile compounds can be separated by the use ofselective columns, but for the usual tests of intoxication, the subjectis held without eating, smoking, or drinking liquids for 20 minutes, anda low resolution column is effective, economical, rapid and unequivocal.

T he present detector with a short polyglycol column is particularlyuseful in receiving rooms of hospi.als. A rapid check can be made forethanol, acetone, gasoline, and various solvents, to distinguishdiabetics, drunks, and poisoning victims, as from carbon tetrachloride,benzene, cleaning fluid, lighter fluid, methanol, etc.

Importantly, subjects which have two or more constituents, as forexample, an intoxicated diabetic; or an intoxicated subject who hasingested methanol or gasoline; or alcohol in the presence of onions,garlic, lemon extract, peppermint oil, or other odors designed todisguise, can have all constituents identified.

The hospital can also determine ether concentrations, both from thestandpoint of depth of anesthetic, and recovery rate, to check ondepartures from normal, after an operation; and explosion hazards.

The use of the flame ion detector in explosion hazards permits checkingof leaks long before a dangerous atmosphere is built up. Flameproofshields can be used around the detector if operation in hazardous areasis contemplated. The use of ether as an industrial solvent isdiscouraged because of its amrnability. With better methods of leakdetection, its industrial use becomes more practical.

Odors and other air pollution can be readily determined, and because ofgreat sensitivity, Sources may be more readily traced.

Water pollution is determined by passing air through a water sample andtesting the air in the arne ion detector. A sample of l microliters to50 microliters of water can be injected, directly, and the water vaporpasses along with the carrier gas, and is not seen in the flame iondetector. If larger quantities of a water sample are needed, theapparatus, including the columns, is heated to keep the water in thevapor phase. Because the flame ion detector is blind to water vapor,this method is particularly useful, as traces of contaminants arelocated even in the presence of large quantities of water vapor and/orcarbon dioxide. Methane, ethane, alcohols, acetone, etc. may be detectedin the presence of each other.

The exhaust gas of a gasoline engine can be analyzed not only from thestandpoint of air pollution, but also to determine combustionefficiency. The exhaust from each cylinder can be independently analyzedto determine if the carburetion efficiency is equal in each cylinder,etc.

For highest accuracy, the hydrogen, nitrogen, and combustion air shouldbe carefully freed from traces of hydrocarbons. A two-stage ormultistage amplifier, and high resistance components in switches, andwiring is required for maximum sensitivity. Around a hospital,background levels of solvents may be so high that a carefully balancedbridge is needed to balance out ambient hydrogen-carbon vapors. Acomparison of inspired air and ex' pired air samples can be used if thebackground level is high. Care must be used to be sure that ambient aircurrents do not change the background levels during l sampling.

In the diagnosis of diabetics, acetone is found in the blood, -urine andbreath of the patient. Insulin is normally used to control the sugarlevel. Analyses were made on several patients Iunder insulin and theacetone concentrations were -found to be about 0.25 p.p.m. Normalconcentration levels were found to vary from 0.10 to 0.50 p.p.m.acetone. One patient who was believed to be in a diabetic coma and hadbeen placed on insulin for several hours was found to have about 50p.p.m. acetone in his breath. (This concentration was lower thanexpected because the patient was hyperventilating and unconscious at thetime the sample was taken.)

With the use of this rapid analytical technique it is possible tomeasure and differentiate many states of diabetic treatment and toobserve the condition of the patient.

Urine, blood and breath samples were analyzed from a diabetic who hadbeen placed on insulin treatment. The acetone content of the urine andblood were found `to be about 0.2 gram of acetone per liter, by passingair over the sample, permitting equilibrium conditions to be reached,and measuring the acetone concentration of the air, and calculatingback. Another -technique is to inject 10 microliters of blood or urinedirectly into the system, and permit solids to drop out on the tubingwalls. The breath sample was found to contain about 1,000 p.p.macetone.High acetone concentrations are indicative of diabetes.

In FIGURE 8 is shown diagrammatically a versatile bridge analyzer forseparately analyzing various components of mixtures either separately orby diiference and which is adaptable to use with various chromatographiccolumns or scrubbing columns to separate a sample gas into selectedfractions. Without unduly repeating the description above in connectionwith other modications, the modification shown in FIGURE 8 has airsupplied through an air reduction valve 102, a control valve 103, to anair T 104, where the flow is split and one portion passed through aneedle valve 105, through an air flow meter 106, and an air flowcapillary 107, into a ame chamber 108. Hydrogen is passed through ahydrogen reduction valve 109, a hydrogen control valve 110, to ahydrogen T 111, where the hydrogen is split into two streams, one ofwhich passes through a hydrogen needle valve 112, a hydrogen ow meter113, and a hydrogen ow capillary 114, to a mixing manifold 115.

A carrier gas, conveniently nitrogen, is passed through a nitrogenreduction valve 116 and a nitrogen control valve 117, through a nitrogenow meter 118, to a nitrogen reservoir 119, which is conveniently a longpiece of coiled tubing, as for example, 12 feet of 1A" OD copper tubing.Connected through a T, at the front end of the tubing is a bubbler 120,conveniently an ar-rn of glass passing into a glass cylinder partiallyfilled with Water which thus limits lthe pressure of nitrogen. Thenitrogen under constant pressure from the nitrogen reservoir 119 flowspast a continuous analysis sample port 121 controlled by a sample valve122 and past an injector septum T 123, which is conveniently a rubberdarn puncturable by a hypodermic needle of the type used in closingpharmaceutical vials to a sample T 124, past a nitrogen and sampleneedle valve 149, and a nitrogen and sample flow meter, through a sampleflow capillary to a sample manifold 126. Between the sample manifold 126and the mixing manifold extends a plurality of chromatographic columnsor absorbent columns 127. These columns have a valve 128 at each end andare interchangeable. Ground glass or inert plastic connectors are used.The substrate on the columns is selected for a particular analysis beingconducted; the details of which are later referred to. The carrier gasand the sample are mixed with hydrogen in the mixing manifold 115 andflow through a trombone 129. This trombone is a pair of glass tubes, atleast one of which is flexibly mounted, one slidably fitting into theother so that the length of the gas path can be controlled. When used ina bridge circuit for differential analysis, it is important that Ithesample from each side 19 of the system reach the ilame ion detectors atthe same time and hence a change in length of flow path is desirable topermit adjustment of the flow time through the sample system. Afterpassing through the trombone the mixture is passed to the electrode jet130. This may be a single jet, or a concentric jet as above described.The collector electrode 131, which may be a wire screen, as abovedescribed, or of other conguration, is in the fla-me chamber above theflame and the conductivity of the flame iS measured.

Two such flame chambers and flow systems complete `are preferred so thatdifferent chromatographic columns or absorbent columns may be used andthe difference in signal measured on a bridge, thus the bridge measuresthe difference in conductivity, and if the ow rates are symmetricalthroughout, the sole difference results from the dilerence in treatmentin the chromatographic columns or absorbent columns 127 and theconcentration of the component which is absorbed can be measureddirectly from the bridge.

One bridge circuit is shown in which a left and a right vacuum tube 132and 133 are connected with a lament battery 134 supplying a filamentcurrent, which lament current s controlled by a lament switch 135. Thecontrol grid of each tube is connected to its respective electrode jet.Also connected to each control grid is a grid resistor 136 whichconveniently can be switched by a grid resistor switch 137 to selectvarious values of grid resistance. The same value is usually used foreach tube of the bridge. From the common point of the grid resistors abias battery 138 is connected to give a negative bias to the controlgrids of the vacuum tubes with respect to the iilaments. From this gridjuncture is also connected a high voltage ybattery 139, the negative endof which is connected to the collector electrodes 131 in each flamechamber. The negative end of a plate battery 140 is also connected tothe common point of the grid resistors. The positive end of the platebattery' is connected to the midpoint of a bridge, convenientlyconsisting of a centring balance potentiometer 141, through a variableresistance 142 and a xed resistance 143 to the plate of the vacuum tube.Conveniently the vacuum tubes may be a CK 5886 with the extra grids tiedto the plate. Bridged across the two plates is a measuring potentiometer144 across one side of which is a recorder resistor 145 and amicroammeter 146, with a protective resistor forming part of themicroammeter. A recorder can be connected across the recorder resistanceto give a recording of the output, or the output can be measured on themicroammeter and the readings recorded manually.

It is to be understood that the bridge circuit shown is one suitablebridge circuit but not the only bridge circuit which will Work. Anyhighly sensitive electrometer circuit can be used. Electrometer circuitsfrom ionization meters are satisfactory, and this art has developed tothe point that stable circuits from ionization meters or Geiger counterscan frequently be purchased as surplus at a marked savings. The detailsof construction of the ame ion detectors is as described earlier in thespecication.

For exibility a xed resistor 147 and a fixed resistor switch 14S areconnected across the collector electrode and the electrode jet of one ofthe ame ion detectors. A

very high resistance, which may be 109 to l015 ohms, is

used so that by closing the switch and turning off one flame, the bridgecircuit can be used to measure the output of the yleft ame ion detectoronly where absolute values rather than diiferential values are desired.

The apparatus as shown is very versatile in that a continuous samplestream may be fed to the continuous analysis sample port 121 and oneportion passed through the left and one portion passed through the rightow controls and ame ion detectors, or individual samples can be injectedthrough the injection septum T121. Where a single sample is injected asa slug, the sample in part backs up into the reservoir 119 andVdisplaces nitrogen through the bubbler 120 without disturbing the dowrates, o1' extinguishing the liame.

A chromatographic column is preferred to separate the components of asmall sample. For continuous ysamples absorption tubes are particularlyuseful. One of the chromatographic or absorption columns 127 is used asa blank with no absorbent but with a volume and flow resistance equal tothat of a chromatographic or absorbent column so that the flow rates arethe same whether an active or inactive column is used. The other columnsare conveniently designed for different analyses. One, for instance B,may have a mixture of 2.0% mercurio sulfate and sulfuric acid, both byweight in water, on a diatomaceous earth absorbent which thus absorbsunsaturated gases. Other columns may have glycerne on diatomaceous earthto separate the various classes such as the hydrocarbons, ethers,aromatics, aldehydes and ketones, alcohols and acids. Other columns mayhave a liquid phase such as methyl phosphoramide, dimethyl sulfolane Vordiisodec ylthalate on them. Thus by changing the control valves betweenthe manifolds a column may be selected for a particular analysis. Eitherdiierential analyses can be run, in which case the bridge gives adifference between the signals from the two columns or one detector canbe turned oi and the xed resistor 147 switched in at 14S and theindividual chromatographic pattern of the sarrid ple determined on theselected column. A fixed resistor having a resistance of the same orderof magnitude as the ame gives good results. I

ln using differential analyses, itis important that the trombone beadjusted so that the ow path on each side of the bridge is the same sothat comparable portions of samples are being compared. The use ofbalanced eapil-j laries, balance ow meters, and generally symmetricalconstruction enhances the ease of such operation, al-v though the needlevalves can be adjusted to modify flow it necessary. The ows should beadjusted so that the same amount of hydrogen, air and nitrogen is beingfed on each side of the bridge so that the sample will be evenly splitand if the same columns are used, a balanced signal would be obtainedeven though the individual signals may be comparatively large.

The size sample to be used depends in par-t upon the sensitivitydesired, `and the concentrations of the materials being measured. Thearea under thecurve is the measure of the concentration, but the heightalone is usually sufficiently accurate and is measured more rapidly.

With a six foot column of glycerine on diatomaceous earth and a nitrogenflow rate of 40 milliliters per minute, as indicative of the timeinvolved, the time from injection to methane was 1.6 minutes. Theremainder of the oleiins and paraflins came off wit-hin the followingtimes after the methane peak, at C.:

Minutes from methane Compound type: peak to peak Olens and parafins0.0-0.2 -Diethyl ether 0.2 Aromatics (C6 to C9) 0.5-1.2 Acetates (loweralkyl) 1.1-1.5 Aldehydes and ketones 2.0-2.5 Alcohols 9.0-14.0 rCarboxyl acids over 2O It is to be stressed that this example isrepresentative of the results which can be obtained. Other columns andiiow rates give dierent absolute and relative results.

We claim:

1. A method for analyzing for classes of carbonhydrogen compoundsindependent of the presence of carbon dioxide and water vapor whichcomprises passing a sample in a carrier gas through a chromatographiccolumn having a polyglycol stationary phase, measuring the conductivityof the effluent carrier gas in ya hydrogen llame, as a function of time,and evaluating serially the classes of compounds in the sample as olensand paraffins, ethers, aromatics, aldehydes and ketones, alcohols, andacids, by measuring the area under a plotted curve of conductivityagainst time for separate peaks on such curve and by comparisonwithknown standards, determining from the time of each peak the identity ofsuch classes of compounds, and from the area of each peak, the quantitypresent.

2. The method of analyzing for carbon-hydrogen compounds in water whichcomprises passing a clean carrier gas through the water thereby elutingdissolved carbonhydrogen compounds, and then passing the carrier gascontaining such carbon-hydrogen compounds into a hydrogen llame,measuring the conductivity of the flame and evaluating as aconcentration of the carbon-hydrogen compounds in the water, saidconductivity being a function of the carbon-hydrogen compound content ofthe carrier gas, and by comparison with known standards, converting todesired units of measurement, the water vapor content of the carrier gasbeing immaterial.

3. The method of claim 2 which comprises passing the carrier gas afterpassing through the water through a chromatographic column and therebyseparating the various carbon-hydrogen compounds, and plotting theconductivity of the hydrogen ame as a function of time, thus separatelyevaluating the various carbon-hydrogen compounds eluted from the water.

4. The vmethod of analyzing for vaporizable carbonhydrogen components ofan aqueous system which comprises injecting a small quantity rof `theaqueous system into an inert carrier gas, depositing non-volatile solidson the walls of a gas transporting means while -vaporizing water andvolatile carbon-hydrogen components, mixing said carrier gas withhydrogen gas, burning the mixture, measuring the conductivity of thellame, and evaluating the carbon-hydrogen content of the aqueous systemfrom the flame conductivity, by comparison with known standards.

5. The method of claim 4 in which the carbon-hydrogen components in saidcarrier gas are passed through a chromatographic column todifferentially retard the passage of, and `thus separate, and renderseparately measurable, the diiferent carbon-hydrogen volatile componentsof the aqueous system.

6. The method of claim 5 in which the aqueous system is selected fromthe group consisting of (a) water suspected of pollution, (b) lblood,and (c) urine.

7. The method of analyzing a body liquid selected from the groupconsisting of blood and urine for vaporizable carbon-hydrogen componentswhich comprises injecting a small quantity of said body liquid into aninert carrier gas, depositing non-volatile solids on the walls of thegas transporting means, vaporizing water and volatile carbonhydrogencomponents, passing said carrier gas through a gas chromatographiccolumn, thereby diierentially retarding the passage of, and -thusseparating, and rendering separately measurable the different volatilecarbon-hydrogen components, mixing the carrier gas with hydrogen gas,burning the mixture, measuring the conductivity of the flame, selectingthe conductivity peaks corresponding to each of ethanol and acetone, andfrom the area under the conductivity-time curve for such peak, ascompared with known standards, calculating and evaluating the ethanoland acetone concentration of the said 'body liquid from the ilameconductivity.

8. A method of detecting and following the course of diabetes comprisingpassing a sample of the subjects breath in a carrier gas through achromatographic column, burning in a hydrogen ame, and measuring theconductivity of the hydrogen -flame at a time corresponding to thepassage of acetone and measuring the area under the conductivity-timecurve for such acetone passage, and by comparison with known standards,converting to acetone concentration in the subjects breath, in desiredunits.

9. A method of detecting and following the course of diabetes comprisingequilibrating a sample of the subjects blood with air, saidequilibration consisting of permitting a volume of air to attainequilibrium conditions with said blood sample, passing a sample of theequilibrated air in a carrier gas through a chromatographic column,burning in a hydrogen flame, and measuring the conductivity of thehydrogen flame at a time corresponding to the passage of acetone andmeasuring the area under the conductivitytime curve for such acetonepassage, and by comparison with known standards converting to acetoneconcentration in the subjects blood, in desired units.

10. -A method of detecting and following the course of diabetescomprising equilibrating a sample of the subjects urine with air, saidequilibration consisting of permitting a volume of air to attainequilibrium conditions with said urine sample, passing a sample of theequilibrated air in a carrier gas ythrough a chromatographic column,burning in a hydrogen flame, and measuring the conductivity of thehydrogen flame at a time corresponding to the passage of acetone andmeasuring the area under the conductivitytime curve for such acetonepassage, and by comparison with known standards, converting to acetoneconcentration in the subjects urine, in desired units.

11. -A method of measuring the change with time of the concentration ofthe carbon-hydrogen and carbonhalogen components of a gas whichcomprises passing one stream of said gas through a yfirst 'flameionization detector, passing a second stream through a delay passage sothat the second stream is measured at a constant time delay with respectto the first stream, then passing said second stream through a duplicatesecond flame ionization detector, said ame ionization detectors beingconnected in a bridge circuit wherein the signals oppose, and readingthe signal difference, which gives a direct reading of the difference inconcentration of the carbon-hydrogen and carbon-halogen content of said:lirst stream and the time delayed said second stream, thus showing thechange in said concentration over the time of the delay.

12. The method of -determining the alcohol content of the human breath,independent of carbon dioxide and water vapor present which comprisespassing a portion of expired human breath through a gas chromatographiccolumn in a carrier stream consisting essentially of an inert gas,eluting the carbon-hydrogen components of the breath in time order,passing the carrier gas containing said components through ahydrogen-oxygen ame, measuring the Vconductivity of the flame as afunction of time, and plotting the same, t-hus differentiating betweenalcohol and other volatile carbon-hydrogen containing compounds in thebreath, and measuring the area under the conductivity-time curvecorresponding to 'the alcohol peak, and by comparison with knownstandards, converting to a measurement in desired units.

13. The method of claim 12 i-n which acetone and ethyl alcohol areseparately evaluated to distinguish between diabetics and intoxicatedpersons.

14. A method of detecting and following the course of diabetes in asubject comprising selecting an acetone containing sample of air fromthe group consisting of the subjects breath, air equilibrated with asample of the subjects blood a-nd air equilibrated with a sample of thesubjects urine, said equilibration consisting of permitting a volume ofair to attain equilibrium conditions with said sample of blood or urine,passing the sample of air in a carrier gas through a gas chromatographiccolumn, burning in a hydrogen dame, and measuring the conductivity ofthe hydrogen lame, plotting the conductivity as a function of time, andby comparison with known standards, selecting the peak corresponding tothe time of passage of acetone, and measuring the area under theconductivitytime curve for such acetone peak, and by comparison withknown standards, converting to acetone concentration in the subject indesired units.

References Cited 24 2,371,637 3/ 1945 `McDermott 23-230 2,511,177`6/1950 Richardson 23-255 2,733,135 1/1956 Hucka'bay 23-230 2,879,663 3/1959 Thomas 73-26 5 3,039,856 6/1962 McWilliam 23-232 3,118,735 1/1964Favre et al 23-232 cember 1949.

Ray, Nature, pp. 40'3-405, August 31, 1957. Heaton et al., Anal. Chem.31, 349-356, March 1959.

JOSEPH SCOVRONEK, Primary Examiner.

UNITED STATES PATENTS 2,192,525 3/1940 Rosaire et al. 23-232 2,591,6914/ 1952 Forrester '23-232 2,901,329 8/1959 Kapff 23-232 2,991,158V7/1961 Harley 23-232 3,049,409 8/ 1962 Dower 23-232 2,084,954 6/ 1937Griswold 23-232 15 MORRIS O. WOLK, Examiner.

D. E. GAN-TZ, Assistant Examiner.

1. A METHOD FOR ANALYZING FOR CLASSES OF CARBONHYDROGEN COMPOUNDSINDEPENDENT OF THE PRESENCE OF CARBON DIOXIDE AND WATER VAPOR WHICHCOMPRISES PASSING A SAMPLE IN A CARRIER GAS THROUGH A CHROMATOGRAPHICCOLUMN HAVING A POLYGLYCOL STATIONARY PHASE, MEASURING THE CONDUCTIVITYOF THE EFFLUENT CARRIER GAS IN A HYDROGEN FLAME, AS A FUNCTION OF TIME,AND EVALUATING SERIALLY THE CLASSES OF COMPOUNDS IN THE SAMPLE ASOLEFINS AND PARAFFINS, ETHERS, AROMATICS, ALDEHYDES AND KETONES,ALCOHOLS, AND ACIDS, BY MEASURING THE AREA UNDER A PLOTTED CURVE OFCONDUCTIVITY AGAINST TIME FOR SEPARATE PEAKS ON SUCH CURVE AND BYCOMPARISON WITH KNOWN STANDARDS, DETERMINING FROM THE TIME OF EACH PEAKTHE IDENTITY OF SUCH CLASSES OF COMPOUNDS, AND FROM THE AREA OF EACHPEAK, THE QUANTITY PRESENT.